U.S. patent application number 10/206198 was filed with the patent office on 2004-01-29 for method for selecting a shading correcting line.
This patent application is currently assigned to UMAX DATA SYSTEMS INC.. Invention is credited to Wang, Kuo-Jeng.
Application Number | 20040017589 10/206198 |
Document ID | / |
Family ID | 30770238 |
Filed Date | 2004-01-29 |
United States Patent
Application |
20040017589 |
Kind Code |
A1 |
Wang, Kuo-Jeng |
January 29, 2004 |
Method for selecting a shading correcting line
Abstract
A method for selecting a shading correcting line is provided.
Scanning a white reference source to obtain several scan lines.
Averaging brightness values of pixels from identical columns in the
scan lines to obtain a new scan line composed of pixels having
median brightness values. Adding one count in shading counting
number when an absolute value of a difference of the median
brightness values between each pair of adjacent pixels in the new
scan line not less than a specification value of shading
definition. Selecting the new scan line as a shading correcting
line when total shading counting number less than a specification
number of shading counts.
Inventors: |
Wang, Kuo-Jeng; (Kaohsiung
City, TW) |
Correspondence
Address: |
LOWE HAUPTMAN GILMAN
& BERNER, LLP
1700 Diagonal Road, Suite 310
Alexandria
VA
22314
US
|
Assignee: |
UMAX DATA SYSTEMS INC.
|
Family ID: |
30770238 |
Appl. No.: |
10/206198 |
Filed: |
July 29, 2002 |
Current U.S.
Class: |
358/461 ;
358/448 |
Current CPC
Class: |
H04N 1/401 20130101 |
Class at
Publication: |
358/461 ;
358/448 |
International
Class: |
H04N 001/40 |
Claims
What is claimed is:
1. A method of selecting a shading correcting line for a bright
image, comprising: scanning a white reference source to obtain a
plurality of first scan lines of pixel brightness values;
generating a second scan line composed of median brightness values
from said first scan lines, each said median brightness value being
an average of said pixel brightness values from a common column of
said first scan lines; adding one count in shading counting number
when an absolute value of a difference of said median brightness
values between each pair of adjacent pixels in said second scan
line being not less than a specification value of shading
definition; and when total shading counting number is less than a
specification number of shading counts, selecting said second scan
line as a shading correcting line.
2. The method of claim 1, wherein said white reference source
comprises a white reference plate.
3. The method of claim 1, wherein said first scan lines are
captured by a charge-coupled device.
4. The method of claim 1, wherein said first scan lines are
captured by a contact image sensor.
5. A method of selecting a shading correcting line for a dark
image, comprising: scanning a black reference source to obtain a
plurality of first scan lines of black reference values; generating
a second scan line composed of median black reference values from
said first scan lines, each said median black reference value being
an average of said black reference values from a common column of
said first scan lines; adding one count in shading counting number
when an absolute value of a difference of said median black
reference values between each pair of adjacent pixels in said
second scan line being not less than a specification value of
shading definition; and when total shading counting number is less
than a specification number of shading counts, selecting said
second scan line as a shading correcting line.
6. The method of claim 5, wherein said black reference source
comprises a black reference plate.
7. The method of claim 5, wherein said first scan lines are
captured by scanning a white reference plate upon turning off a
light source.
8. The method of claim 5, wherein said first scan lines are
captured by scanning a white reference plate upon using a shading
plate to shade a light receiving plane of a photosensitive
detector.
9. The method of claim 8, wherein said photosensitive detector
comprises a linear charged-coupled device.
10. The method of claim 8, wherein said photosensitive detector
comprises a contact image sensor.
11. A method for judging shading of an image, comprising: scanning
an image to obtain a plurality of first scan lines each of which
having several pixel values; generating a second scan line composed
of median pixel values from said first scan lines, each said median
pixel value being an average of said pixel values from a common
column of said first scan lines; adding one count in shading
counting number when an absolute value of a difference of said
median pixel values between each pair of adjacent pixels in said
second scan line being not less than a specification value of
shading definition; and when total shading counting number is less
than a specification number of shading counts, said image is
allowable.
12. The method of claim 11, wherein said image comprises a bright
image.
13. The method of claim 11, wherein said image comprises a dark
image.
14. The method of claim 11, wherein said first scan lines are
captured by a charge-coupled device.
15. The method of claim 11, wherein said first scan lines are
captured by a contact image sensor.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a shading correction method
for reducing non-uniformity in the density of a read image in an
image reading apparatus such as a facsimile or an image
scanner.
[0003] 2. Description of the Prior Art
[0004] Conventional color image reading apparatuses generally scan
an original placed on a transparent platen mainly composed of glass
with light emitted from a light source and receive light reflected
from the original to read an image on the original. For reading a
color image, the image reading apparatus resolves the reflected
light by some means into three components of light, i.e. R (red), G
(green) and B (blue), and directs the three components on a
light-receiving section of a photoelectric converter such as a CCD
(charge-coupled device), which serves as a reading element, so as
to convert them into analog electric signals of the three
components R, G, and B. The signals are then outputted in the form
of digital electric signals by means such as an A/D converter.
[0005] In the above-described image reading apparatus, there arises
a phenomenon called shading distortion owing to various causes such
as variations in quantity of light from the light source,
variations in conversion characteristics of photoelectric
conversion elements defining pixels, changes in quantity of light
from the light source caused by changes of voltage in the device,
changes in the conversion characteristics of the photoelectric
conversion elements with time, and variations in quantity of light
passing through a lens for forming images. The shading distortion
means that the electric signals outputted by the photoelectric
converter vary and do not represent a constant value even if an
image of a consistent shade of color is taken by the image reading
apparatus through optical scanning and directed to the
photoelectric converter.
[0006] Various attempts have been made for the correction of the
shading distortion to minimize variations in outputted signals and
always obtain constant electric signals, regardless of the
above-mentioned causes, when reading an image of the consistent
shade. Such correction is called shading correction.
[0007] This shading correction is to be performed before reading an
image of the original for correcting the light receiving data with
use of white reference data obtained from the photoelectric
conversion elements upon receiving reflected light from a white
reference plate and black reference data obtained from the
photoelectric conversion elements when the photoelectric conversion
elements are shaded.
[0008] A generally employed method for shading correction is
setting a reference white sheet for white balance in a place other
than the original platen on a travel path of an optical system
which optically scans and reads an image of the original. This
reference white sheet is optically scanned and the image thereof is
read by the photoelectric converter before the original is
optically scanned. On the basis of data of this read image,
correction values for the signals representative of the R, G and B
components are calculated for every photoelectric conversion
element defining a pixel. Data of the read original is corrected by
adding the calculated correction values.
[0009] However, it is not always possible to perform an optimum
shading correction as it is likely the case such as the reference
white sheet is not in a mint condition or electrical noise maybe
picked up, rendering to degrade reliability of the white reference
data and the black reference data. This in turn results in
disabling the proper shading correction.
[0010] Accordingly, it is an intention to provide a method of
shading correction, which can improve shading correction operated
on a read image based on good shading correction values, and thus
obtaining an outputted image with a high degree of reliability.
SUMMARY OF THE INVENTION
[0011] It is one objective of the present invention to provide a
method for selecting a shading correcting line, which makes shading
correction based on good shading correction values, thereby being
capable of obtaining a good shading-corrected image.
[0012] It is another objective of the present invention to provide
a method for selecting a shading correcting line, which makes it
possible to enable image reading performed with a high degree of
reliability.
[0013] It is a further objective of the present invention to
provide a method for selecting a shading correcting line, which is
capable of removing adverse effects due to impulse noise or dust
that is accumulated on a white reference plate.
[0014] It is still a further objective of the present invention to
provide a method for judging shading of an image, which can
calculate an exact shading counting number of the image, and
accordingly judging whether to utilize the image.
[0015] In order to achieve the above objectives of this invention,
the present invention provides a method for selecting a shading
correcting line. Scanning a white reference source to obtain a
plurality of first scan lines of pixel brightness values.
Generating a second scan line composed of median brightness values
from the first scan lines, each median brightness value being an
average of pixel brightness values from a common column of the
first scan lines. Adding one count in shading counting number when
an absolute value of a difference of median brightness values
between each pair of adjacent pixels in the second scan line being
not less than a specification value of shading definition. When
total shading counting number is less than a specification number
of shading counts, selecting the second scan line as a shading
correcting line. In accordance with the present invention, a
shading correction operation based on good shading correction
values is implemented, and thereby being capable of obtaining a
good shading-corrected image.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The objectives and features of the present invention as well
as advantages thereof will become apparent from the following
detailed description, considered in conjunction with the
accompanying drawings.
[0017] FIG. 1 is a schematic diagram of a document feeder unit of
an image reading apparatus;
[0018] FIGS. 2A and 2B is a flow chart of the present method
according to one embodiment of the present invention; and
[0019] FIG. 3 schematically illustrates steps of selecting a
shading correcting line in accordance with the principle of the
present invention.
DESCRIPTION OF THE EMBODIMENTS
[0020] FIG. 1 is a schematic diagram of a document feeder unit 10
of an image reading apparatus used for illustrating the present
method. The document feeder unit 10 includes a white reference
plate 100, an exposure lamp 101, a lamp driving unit (not shown),
an optical system including reflection mirrors 102-104 and a focus
lens 105, a shading plate 106, a shading plate drive unit (not
shown), a photoelectric linear sensor 107, and a transparent platen
(not shown) on which a document 108 is placed.
[0021] The white reference plate 100 is used to obtain white
reference data for use in a shading correction and is provided in
an area next to the document 108 which is placed on the transparent
platen, as shown in FIG. 1.
[0022] The exposure lamp 101 consists of a fluorescent lamp or a
halogen lamp to emit light to the white reference plate 100 and the
document 108. The lamp drive unit (not shown) is to illuminate the
exposure lamp 101 and is to move the same along an arrow A (in FIG.
1) to illuminate the entire surface of the document 108 along the
arrow A.
[0023] The optical system including reflection mirrors 102-104 and
the focus lens 105 to lead the reflected light from the document
108 to the photoelectric linear sensor 107 to form an image on its
light-receiving plane.
[0024] The shading plate 106 is to shade the light-receiving plane
of the photoelectric linear sensor 107 to obtain black reference
data for use in a shading correction.
[0025] The photoelectric linear sensor 107 can be a CCD
(charge-coupled device) line sensor or a contact image sensor (CIS)
to output analog voltage signals. And, an A/D converter (not shown)
is to convert the analog voltage signals to 8 bit digital signals.
This read image data of 8 bit digital signals is subjected to a
shading correction operation based on shading correction values
from a shading correcting line selected in accordance with the
present method.
[0026] Alternately, the black reference data can be obtained by
turning the exposure lamp 101 off to cause the photoelectric linear
sensor 107 to perform a reading operation. In producing the black
reference data, the exposure lamp 101 is turned off. In the state,
reflected light from the white reference plate 100 is read. Since
the white reference plate 100 is not illuminated, there is no
reflected light from the white reference plate 100, whereby the
photoelectric linear sensor 107 captures the black reference
data.
[0027] The present method of selecting a shading line established
by the white reference data or black reference data will be
described in detail in accordance with one embodiment of the
present invention.
[0028] FIGS. 2A and 2B is a flow chart of the present method
according to the embodiment. FIG. 3 schematically illustrates steps
of selecting a shading correcting line in accordance with the
principle of the present invention. Initially, at step 200,
scanning a white reference source, such as a white reference plate,
to obtain a plurality of scan lines, such as L.sub.1, L.sub.2 and
L.sub.3 (see FIG. 3), each of which composed of pixel brightness
values (P.sub.1,1, P.sub.1,2, P.sub.1,3, P.sub.1,4, P.sub.1,5 . . .
P.sub.1,n), (P.sub.2,1, P.sub.2,2, P.sub.2,3, P.sub.2,4, P.sub.2,5
. . . , P.sub.2,n), and (P.sub.3,1, P.sub.3,2, P.sub.3,3,
P.sub.3,4, P.sub.3,5 . . . , P.sub.3,n), respectively. However, the
number of the scan lines is not limited to only three, any other
number is also acceptable. Then, at step 201, generating a new scan
line L.sub.avg composed of median brightness values (P.sub.1,avg,
P.sub.2,avg, P.sub.3,avg, P.sub.4,avg, P.sub.5,avg . . . ,
P.sub.n,avg) from the scan lines L.sub.1, L.sub.2 and L.sub.3 (see
FIG. 3). Each median brightness value is an average of the pixel
brightness values from a common column of the scan lines L.sub.1,
L.sub.2 and L.sub.3. For example, P.sub.2,avg is an average of the
pixels brightness values P.sub.1,2, P.sub.2,2 and P.sub.3,2.
Subsequently, at step 202, taking an absolute value of a difference
of median brightness values between each pair of adjacent pixels in
the new scan line L.sub.avg, for example, .vertline..DELTA.P.sub.2,
3.vertline., .vertline..DELTA.P.sub.4, 5.vertline. etc (see FIG.
3). At step 203, adding one count in shading counting number when
the absolute value is not less than a specification value of
shading definition. Then, at step 204, judging if total shading
counting number of the new scan line L.sub.avg is not less than a
specification number of shading counts. If it is yes, the new scan
line L.sub.avg is abandoned (step 205). If it is not, the new scan
line L.sub.avg is selected as a shading correcting line. The
shading correcting line has good shading correction values. And,
after the shading correcting line is established, image data are
read, and the read image data are subjected to shading correction
on the basis of the shading correction values of the selected
shading correcting line.
[0029] As to a shading correcting line from black reference data,
at step 200 of FIG. 2A, a black reference source is scanned to
obtain a plurality of scan lines of pixel brightness values. The
black reference source can be provided by way of shading the
photoelectric linear sensor 107 with the shading plate 106.
Alternately, by turning off the exposure lamp 101 and causing the
photoelectric linear sensor 107 to perform a reading operation upon
the white reference plate 100. Steps 201, 202, 203, 204, 205 and
206 are then followed so as to obtain a shading correcting line
generated from the black reference data.
[0030] In another aspect of the present invention, according to the
flow chart of FIG. 2A and FIG. 2B, the present invention can
calculate exact shading counting number of a captured bright image
or dark image, and thereby judging whether the captured bright
image or dark image can be used. Thus, the present invention can
obtain an image with better quality. Following is a detailed
description. Initially, at step 200, a bright image is instead of
the white reference source, scanning the bright image to obtain a
plurality of scan lines, such as L.sub.1, L.sub.2 and L.sub.3 (see
FIG. 3), each of which composed of pixel brightness values
(P.sub.1,1 , P.sub.1,2, P.sub.1,3, P.sub.1,4, P.sub.1,5. . . ,
P.sub.1,n), (P.sub.2,1, P.sub.2,2, P.sub.2,3, P.sub.2,4, P.sub.2,5
. . . , P.sub.2,n), and (P.sub.3,1, P.sub.3,2, P.sub.3,3,
P.sub.3,4, P.sub.3,5 . . . , P.sub.3,n), respectively. However, the
number of the scan lines is not limited to only three, any other
number is also acceptable. Then, at step 201, generating a new scan
line L.sub.avg composed of median brightness values (P.sub.1,avg,
P.sub.2,avg, P.sub.3,avg, P.sub.4,avg, P.sub.5,avg . . .
P.sub.n,avg) from the scan lines L.sub.1, L.sub.2 and L.sub.3 (see
FIG. 3). Each median brightness value is an average of the pixel
brightness values from a common column of the scan lines L.sub.1,
L.sub.2 and L.sub.3. For example, P.sub.2,avg is an average of the
pixels brightness values P.sub.1,2, P.sub.2,2 and P.sub.3,2.
Subsequently, at step 202, taking an absolute value of a difference
of median brightness values between each pair of adjacent pixels in
the new scan line L.sub.avg, for example, .vertline..DELTA.P.sub.2,
3.vertline., .vertline..DELTA.P.sub.4, 5.vertline. etc (see FIG.
3). At step 203, adding one count in shading counting number when
the absolute value is not less than a specification value of
shading definition. Then, at step 204, judging if total shading
counting number of the new scan line L.sub.avg is less than a
specification number of shading counts. If it is not, the bright
image captured at step 200 is abandoned (step 205). If it is yes,
the bright image captured at step 200 is allowable.
[0031] As to how to calculate exact shading counting number of a
dark image, at step 200, the dark image is instead of the bright
image, scanning the dark image to obtain a plurality of scan lines
of pixel brightness values. Steps 201, 202, 203, 204, 205 and 206
are then followed. At step 204, judging if total shading counting
number of the new scan line L.sub.avg is less than a specification
number of shading counts. If it is not, the dark image captured at
step 200 is abandoned (step 205). If it is yes, the dark image
captured at step 200 is allowable.
[0032] In accordance with the above described, the present
invention makes a shading correction operation based on good
shading correction values, thereby being capable of obtaining a
good shading-corrected image. It is also possible to enable image
reading performed with a high degree of reliability. The adverse
effects due to impulse noise or dust that is accumulated on a white
reference plate also can be removed.
[0033] The embodiments are only used to illustrate the present
invention, not intended to limit the scope thereof. Many
modifications of the embodiments can be made without departing from
the spirit of the present invention.
* * * * *